JPS6252251B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is based on the optical pulse echo method.
This invention relates to an echo detection device.

Optical fibers are effective when applied to long-distance, high-capacity communication systems by taking advantage of their low loss properties, and specific applications are beginning to be considered for backbone transmission lines and international long-distance submarine cable transmission lines. In these long-distance systems, it is important to have technology to test for transmission line failures such as optical fiber breaks beforehand before or after cable manufacturing or installation, or to locate failures in the event of a failure.・There is a strong need for the development of an optical pulse-echo detection device that applies the pulse-echo method used in optical communication systems to optical communication systems. In particular, low loss (0.2
In the case of optical fiber (~1 dB/Km), the reflectance in the air is about 3.5% at most, and about 0.2% at most in seawater, so techniques for amplifying weak signals and reducing noise are needed. Techniques for improving the signal-to-noise ratio are becoming important.

As shown in Fig. 1, a conventional optical pulse/echo detection device uses an optical branching section 1 of three optical input/output terminals (hereinafter referred to as "ports") to detect optical pulses from a light emitting source 2 such as a laser. Optical fiber 4 with point 3
The optical pulse reflected at the failure point 3 is divided into two by the half mirror 5 in the optical branching section 1, a part of which enters the photodetector 6, where it is converted into an electrical signal and then sent to the amplifier. 7, the signal is amplified by a noise processor 8 that uses an integral effect to extract only the signal component, and then displayed on a display device 9 such as an oscilloscope.The signal is then displayed on a display device 9 such as an oscilloscope. I was looking for it. However, with this configuration,
Reflection from the prism or half mirror placed in the optical branch 1 or the end face of the optical fiber connected to each port is unavoidable, and this reflected pulse becomes a weak reflected pulse from the failure point 3. The disadvantage is that the amplifier 7 becomes saturated and the reflected pulse cannot be sufficiently amplified because it is very large compared to the other two, and optical branching using a half mirror or prism is required to separate the transmitted optical signal and the received optical signal. Because part 1 is used, the reflected pulse will theoretically suffer from an insertion loss of 6 dB compared to the transmitted optical signal, which has the disadvantage of reducing the signal-to-noise ratio.

To address these shortcomings, methods have been proposed that do not generate unnecessary reflected pulses and reduce the theoretical loss to half of the conventional one (see IEICE Technical Report CS79-17), There is no difference in the fact that

The present invention provides an optical pulse/echo detection device which has an excellent signal-to-noise ratio and uses an optical branching means that has no unnecessary reflected pulses from the optical branching means and, in principle, no insertion loss.

To achieve this objective, the optical pulse echo detection device of the present invention is configured such that in the first state, the first and second ports are electrically connected, and in the second state, the second and third ports are electrically conductive. A three-port optical branching device using electric or acousto-optic elements adjusted to After connecting each of the photodetectors, it is configured such that the light pulse from the light emitting source is in the first state until it passes through the light branching device, and immediately switches to the second state after passing through the light branching device. It is a feature.

The present invention will be explained in detail below using the drawings.

FIG. 2 shows an embodiment of the present invention, in which a light pulse sent out from a light emitting source 2 enters the inside of the optical branching device 11 through the first port 10 of the optical branching device 11.
There, it is deflected by an electric or acousto-optic element 15 and enters the optical fiber 4 connected to the second port 12 . At this time, a deflection signal supply source 13 that supplies an electric signal for deflection to the electric or acousto-optic element 15 in synchronization with the driving pulse of the light emitting source 2 transmits the optical pulse sent from the light emitting source 2 to the optical branching device 11.
The configuration is such that the deflection signal is supplied only during the time it passes through, and thereafter the deflection signal is turned off. With current technology, deflections of approximately 10 degrees can be achieved in a few nanoseconds. A part of the optical pulse sent to the optical fiber 4 is reflected at the failure point 3, passes through the optical fiber 4 again, and enters the optical branching device 11 from the second port, but at this time, as is clear from the above explanation, Electric or acousto-optic elements 15
Since no deflection signal is applied to
The light then reaches the photodetector 6.

An electro-optical element can be realized by applying a DC electric field of appropriate strength to a material having an electro-optic effect such as LiNbO ₃ or LiTaO ₃ and passing light through this material. The optical element can be realized by forming a material having an acousto-optic effect such as LiNbO ₃ so as to apply an ultrasonic wave of appropriate intensity, and then passing light through this material.

Since the optical pulse/echo detection device according to the present invention operates as described above, it has the advantage that there are no unnecessary reflected pulses from the optical branching section, and insertion loss can also be eliminated in principle. This is an optical pulse/echo detection device with excellent noise ratio.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing an example of a conventional device; Figure 2 is a block diagram showing an example of a conventional device;
The figure is a block diagram showing an embodiment of the present invention. 1, 11... Light branching section, 2... Light emitting source, 3...
Failure point, 4... Optical fiber, 5... Half mirror, 6... Photodetector, 7... Amplifier, 8... Noise processor, 9... Oscilloscope, 10, 12, 1
4...Port, 13...Deflection signal source.

Claims (1)

[Claims] 1 Send a light pulse from a light pulse emission source to an optical fiber to be measured, detect a reflected pulse reflected at a fault point of the optical fiber to be measured by a reflected pulse detection means, and detect the reflected pulse from the time of sending out the light pulse. In the optical pulse/echo detection device configured to locate the failure point based on the time difference between detection of reflected pulses, an optical pulse echo detector is provided between the optical pulse emission source, the optical fiber to be measured, and the reflected pulse detection means. an optical branch that forms an optical path between the optical pulse emission source and the optical fiber to be measured in a first state, and forms an optical path between the optical fiber to be measured and the reflected pulse detection means in a second state; In addition to providing means,
Control means for setting the light branching means in the first state to cause the light pulse emission source to emit light pulses, and setting the light branching means in the second state after a predetermined time elapses after the light emission. An optical pulse/echo detection device characterized by being provided with.